The first option:
"Big buttons" - The template is going to use different graphics for "normal" and "big" buttons. To know when a button is "normal" or when is "big", the template will use the value entered here. Buttons which height is more than this will be considered "big", the others will be considered "small" (as opposite of "big", but they are in fact "normal" buttons). A value up to 20 uses to work fine here.
You may think "Why don't use big buttons all the time? After all, they look fine." Yes, but the problem is that "big" buttons place a lot of overhead in your program, as more bytes should be read over and over each time a window is draw. While this may not be noticed in newer and fast machines, it certainly do in older ones.